/python-async

name: python-async
description: Async Python patterns via asyncio and aiohttp for I/O-bound concurrency. Use when adding async APIs, handling concurrent I/O, or debugging async code.
globs: "**/*.py"
alwaysApply: false
category: async
tags:
- python
- async
- asyncio
- concurrency
- await
- coroutines
tools: []
usage_patterns:
- async-api-development
- concurrent-io
- websocket-servers
- background-tasks
complexity: intermediate
estimated_tokens: 400
progressive_loading: true
modules:
- modules/basic-patterns.md
- modules/concurrency-control.md
- modules/error-handling-timeouts.md
- modules/advanced-patterns.md
- modules/testing-async.md
- modules/real-world-applications.md
- modules/pitfalls-best-practices.md

Async Python Patterns

asyncio and async/await patterns for Python applications.

Quick Start

import asyncio

async def main():
    print("Hello")
    await asyncio.sleep(1)
    print("World")

asyncio.run(main())

When To Use

• Building async web APIs (FastAPI, aiohttp)
• Implementing concurrent I/O operations
• Creating web scrapers with concurrent requests
• Developing real-time applications (WebSockets)
• Processing multiple independent tasks simultaneously
• Building microservices with async communication

When NOT To Use

• CPU-bound optimization - use python-performance instead
• Testing async code - use python-testing async module

Modules

This skill uses progressive loading. Content is organized into focused modules:

• See `modules/basic-patterns.md` - Core async/await, gather(), and task management
• See `modules/concurrency-control.md` - Semaphores and locks for rate limiting
• See `modules/error-handling-timeouts.md` - Error handling, timeouts, and cancellation
• See `modules/advanced-patterns.md` - Context managers, iterators, producer-consumer
• See `modules/testing-async.md` - Testing with pytest-asyncio
• See `modules/real-world-applications.md` - Web scraping and database operations
• See `modules/pitfalls-best-practices.md` - Common mistakes and best practices

Load specific modules based on your needs, or reference all for detailed guidance.

Exit Criteria

• [ ] Async patterns applied correctly
• [ ] No blocking operations in async code
• [ ] Proper error handling implemented
• [ ] Rate limiting configured where needed
• [ ] Tests pass with pytest-asyncio

Troubleshooting

Common Issues

**RuntimeError: no current event loop** Use `asyncio.run()` as the entry point. Avoid `get_event_loop()` in Python 3.10+.

**Blocking call in async context** Move sync I/O to `asyncio.to_thread()` or `loop.run_in_executor()`.

**Tests hang indefinitely** Ensure pytest-asyncio is installed and test functions are decorated with `@pytest.mark.asyncio`.